1. Field of the Invention
This invention relates generally to an automotive manual transmission and especially to a transmission mechanism that is transversely disposed with respect to the fore-and-aft axis of the vehicle.
2. Description of the Prior Art
When the engine of a motor vehicle is idling and the neutral clutch that connects the engine to a manual transmission is disengaged, the speed of the engine varies as a result of the cyclic irregularity that is intrinsic in the operation of an internal combustion engine. Countershaft manual transmissions for automotive use contain gearsets whose members are in continuous meshing engagement, though the gear selector to the transmission is in the neutral position. When the neutral clutch is engaged and the gear selector is in the neutral position, the speed changes of the engine transmitted to the gearset produce noise called gear rattle. When the engaged gear teeth change position with respect to each other due to the engine speed variations, the teeth of the driven gear contact alternately the driving face and the non-driving face of the driving pinion.
To reduce or eliminate the objectionable noise that results from this contact, various devices have been employed to take up the clearance between the faces of the gear and the mating pinion. These devices include a wheel coaxial with the gear having similar teeth to those of the gear and means for elastically maintaining the teeth of the gear in a position that is angularly offset relative to the gear. Usually in such devices, a mechanical spring, such as a helical spring, located radially offset from the axis of the gear, applies a force directed tangentially to the axis and tending to rotate the annular element with respect to the gear wheel. Other means than helical springs, such as elastomeric material, have been used in the prior art to bias an annular member angularly with respect to the gear to maintain contact between mating gear teeth in order to avoid gear rattle.
In addition to neutral rollover gear rattle, an additional gear rattle condition is known to occur particularly in fourth of fifth gear ratio operation with the engine under load and operating at a speed that is sufficient low as to cause engine lugging. In these conditions, the torsional vibrations of the engine are exceptionally strong and cause excessive vibration. Within the transmission they cause a rattle or chattering sound to issue from the transmission due to contact being made on opposite faces of engaged gears and pinions.